In the treatment of porous, fibrous material with gas it is desirable to minimize the comsumption of gas while at the same time providing optimum intermixing of, and contact between, the material and the gas in order to effect uniform, efficient treatment. This is especially so in treating cellulosic fiber pulp with a treatment gas, such as a gas containing ozone, during oxygen delignification of the pulp, or the like. This is most often accomplished by causing the pulp and gas to flow downwardly in a reacting vessel, and interrupting the column of pulp at various points to prevent compaction of the pulp, and to attempt to provide uniform access of the gas to the material.
According to the present invention a method and apparatus for the continuous treatment of a fibrous material with gas is provided that maximizes the uniformity and efficiency of treatment, and does so in a relatively simple manner. According to the invention, instead of the material and gas remaining continuously in contact together in a common flow path, the flows of the gas and material are separated, and then the path of the material is caused to intersect the continuous flow path of gas one or more times. Since a continuous stream of gas is utilized, maximum efficiency of the gas treatment is obtained, and due to the intersection nature of the material and gas path intimate mixing of the gas and material, with resultant uniform treatment of the material, takes place.
According to one aspect of the method according to the invention, a porous fibrous material is treated with gas according to the following sequential continuous steps: The material is entrained with gas and passed in a first path. The material is substantially separated from the gas so that the material flows in a second path and the gas flows in a third path, distinct from the second path. The material moves in the second path so that it intersects the flow of gas in the third path at least once, with the gas passing through the material while remaining in the third path, distinct from the second path, until the desired treatment of the material with gas has been achieved. Then the material is moved in a fourth path, and the gas in a fifth path, entirely distinct from the fourth path.
Preferably the second path is a serpentine path having substantially horizontal portions interconnected by curved portions, and the third path is a substantially straight path extending downwardly, and intersecting the horizontal portions of the second path. The gas is caused to flow in the third and fifth path under the influence of a slight overpressure, and a suction device disposed in the fifth path, and the second path is preferably defined by a plurality of air-pervious conveyor belts. The material and gas are initially separated by causing them to move in a path defined by a downwardly curved upper wall and an open bottom, with a baffle disposed adjacent the bottom termination of the downwardly curved wall. The material continues to follow the wall and discharge onto one of the conveyor belts, while the gas does not tend to continue along the wall, but rather discharges into the open bottom of the separation path.
The preferred material treatment apparatus according to the invention comprises a plurality of conveying assemblies, each assembly comprising an endless air-pervious belt having a plurality of conveying projections extending outwardly therefrom, and having first and second end rollers about which the belt moves. Means are provided for mounting the rollers of each of the belts so that they are rotatable about substantially horizontal axes that are parallel to each other and are both disposed in a substantially horizontal common plane, and for mounting the assemblies vertically spaced from each other and in vertical alignment. Means are also provided for rotating the rollers of the conveying assembly so that the rollers of one assembly rotate in the opposite direction from the rollers of the vertically adjacent assembly, and further means defining a substantially vertical gas passageway through and between each assembly are provided.
It is the primary object of the present invention to provide an efficient method and apparatus for the uniform treatment of porous fibrous material with gas, particularly fluffed cellulosic fiber pulp with a gas containing ozone. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.